In oil exploration or drilling operations, drilling fluids are commonly used but would be lost due to penetration into the formation soil under pressure, the process of which is generally referred to as “water loss”. A large amount of water loss into the soil will not only lead to the problem of borehole instability, but also harm the hydrocarbon reservoir. Currently, one solution to this problem is to add a filtration control agent in the drilling fluids. The filtration control agent has the following functions. It can comprehensively block capillary channels in a mud cake that is formed by the drilling fluid and the soil, making the mud cake smooth and compact, and can increase negative charge density on the mud cake to form a strong polarization water layer. Molecules of the filtration control agent can be absorbed on one side of clay crystal particles to form a bridging therebetween which can narrow down the pore size of the capillary channel. The filtration control agent can further improve wettability of the capillary channel in the mud cake. Therefore, the filtration control agent can enhance the filtration-reducing ability of the drilling fluid. Filtration control agent polymers commonly used at present in drilling fluids, on the other hand, have poor temperature resistance and salt resistance and poor chemical stability, and therefore are easily subject to hydrolysis under high temperatures. This would decrease the molecular weight of the polymers and render them ineffective.